r312452-r312512:

- Use SRCTOP-relative paths to other directories instead of .CURDIR-relative ones

  This simplifies pathing in make/displayed output

- Use .CURDIR:H instead of .CURDIR to simplify pathing in output, etc

directly create the socket with SOCK_NONBLOCK instead of calling fcntl(2)

Sponsored by:	EMC / Isilon Storage Division

lib/libdevdctl/consumer.cc
	In Consumer::DisconnectFromDevd, don't close the socket if it's
	already closed.

cddl/usr.sbin/zfsd/case_file.cc
lib/libdevdctl/consumer.h
	Delete dead code leftover from before devd(8) gained SOCK_SEQPACKET
	support

Reported by:	Coverity
CID:		1356155, 1356169
Sponsored by:	Spectra Logic Corp

Add zfsd, which deals with hard drive faults in ZFS pools. It manages
hotspares and replements in drive slots that publish physical paths.

cddl/usr.sbin/zfsd
	Add zfsd(8) and its unit tests

cddl/usr.sbin/Makefile
	Add zfsd to the build

lib/libdevdctl
	A C++ library that helps devd clients process events

lib/Makefile
share/mk/bsd.libnames.mk
share/mk/src.libnames.mk
	Add libdevdctl to the build. It's a private library, unusable by
	out-of-tree software.

etc/defaults/rc.conf
	By default, set zfsd_enable to NO

etc/mtree/BSD.include.dist
	Add a directory for libdevdctl's include files

etc/mtree/BSD.tests.dist
	Add a directory for zfsd's unit tests

etc/mtree/BSD.var.dist
	Add /var/db/zfsd/cases, where zfsd stores case files while it's shut
	down.

etc/rc.d/Makefile
etc/rc.d/zfsd
	Add zfsd's rc script

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev.c
	Fix the resource.fs.zfs.statechange message. It had a number of
	problems:

	It was only being emitted on a transition to the HEALTHY state.
	That made it impossible for zfsd to take actions based on drives
	getting sicker.

	It compared the new state to vdev_prevstate, which is the state that
	the vdev had the last time it was opened.  That doesn't make sense,
	because a vdev can change state multiple times without being
	reopened.

	vdev_set_state contains logic that will change the device's new
	state based on various conditions.  However, the statechange event
	was being posted _before_ that logic took effect.  Now it's being
	posted after.

Submitted by:	gibbs, asomers, mav, allanjude
Reviewed by:	mav, delphij
Relnotes:	yes
Sponsored by:	Spectra Logic Corp, iX Systems
Differential Revision:	https://reviews.freebsd.org/D6564